Visible Light-assisted Reduction Of CO₂ Over Post-modified NH₂-MIL-125（Ti） Catalysts

The utilization of CO₂ could not only solve the environmental problems caused by the greenhouse effect,but also relieve the resources shortage.Photocatalytic CO₂ fixation has been becoming one of the most promising solutions to mitigate CO₂ emissions.Therefore,to the efficient utilization of CO₂ by photocatalytic reduction technology,the development of new visible-light-induced photocatalysts is considered as a important step.Metal-organic frameworks（MOFs）represent a new class of hybrid porous materials with:（a）highly ordered pore structure and dispersive pore channel,lots of the active sites;（b）high surface area and free pore volume,low crystal density;（c）easy to design,diverse structure,modify and modulate,in which make them attractive in photocatalysis.But the great potential of MOFs as photocatalysts is still a few appreciated.In the thesis,NH₂-MIL-125（Ti）was modified with either metallic Co nanoparticles（NPs）or 2-pyridaldehyde（PA）based on its structure features.Then the prepared samples were characterized by some techniques such as XRD,XPS,UV-vis DRS,photoluminescence,photocurrent and so on.Furthermore,the synthesized catalysts were used in the reduction of CO₂ upon visible light irradiation.Additionally,the mechanism of the photocatalytic reduction of CO₂ over Co/NH₂-MIL-125（Ti）has been proposed.The main results are summarized as bellow:1.Compared with NH₂-MIL-125（Ti）,Co/NH₂-MIL-125（Ti）catalysts exhibit an enhanced activity in the photocatalytic reduction of C℃2 using triethanolamine（TEOA）as the sacrificial agent.The optimum content of the Co NPs in NH₂-MIL-125（Ti）is about 1.0 wt.%for the photocatalytic reduction of C℃2 with about 38.4 μmol gcat-1 h-1 of the produced HCOOH.Furthermore,aromatic alcohols,instead of triethanolamine that is often used as the sacrificial agent,can be oxidized to the corresponding aldehydes during the photocatalytic reduction of CO₂,making the proposed process more economical and environment-friendly.2.The PA modified photocatalyst[PA/NH₂-MIL-125（Ti）]has an enhanced absorption capacity under the visible-light region,compared with NH₂-MIL-125（Ti）.Upon visible light irridiation,PA/NH₂-MIL-125（Ti）can selectively catalyze the reduction of CO₂.Compared with NH₂-MIL-125（Ti）,its photocatalytic activity is big improved.3.In combination with extensive characterizations by various techniques,it is found that the doping of the Co NPs encapsulated in NH₂-MIL-125（Ti）can enhance the visible-light harvesting and electron transfer,leading to a higher photocatalytic activity.Novelty of the thesis research:on the one hand,the photocatalytic activity of the reduction of CO₂ could be significantly enhanced by the post-modification of NH₂-MIL-125（Ti）,with either metallic Co NPs or PA;on the other hand,the photocatalytic reduction of CO₂ coupled with the selective oxidation of aromatic alcohols has been achieved for the first time.These results can provide a new avenue for development of novel visible-light-driven photocatalysts and also broaden the application of MOFs and enrich the theory of the photocatalytic CO₂ fixation.